The ASPEN CANCER CONFERENCE, a series of yearly meetings emphasizes the relationships between toxicity, cell injury, and carcinogenesis. The purpose of these meetings is and continues to be to assemble a group of leading scientists working in a wide range of disciplines and representing industry, government and academia to confer formally and informally on current concepts and aspects of research which transcend normal boundaries. During recent years, the emphasis has focused increasingly on the molecular aspects of toxicity and carcinogenesis , and the relationship between the two as they relate to human risk. The formal consists of invited presentations and discussions in the mornings, and poster sessions and informal discussions in the afternoons and evenings, fostered by the environment provided in Aspen, Colorado. One of our goals is to sponsor attendance by post-doctoral fellows, graduate students, medical students and veterinary students, with special efforts being made to guarantee diversity. We have encouraged the participation and young investigators and include poster sessions in alternative years through which informal contact in mutual areas of interest can be made with established investigators. This, along with sessions on the applications of new technology in related areas of research, should assist greatly in future developments in these fields. The 1999 ASPEN CANCER CONFERENCE: Mechanisms of Toxicity and Carcinogenesis will consider mechanisms of toxicity, growth control, and differentiation, as well as strategies for toxicity and carcinogenesis testing and innovative approaches to cancer chemotherapy; specifically: Signaling Pathways as Targets for Therapy and Prevention; Chronic Tissue Injury; Microbial Oncogenesis; Genetic Instability; Predictive Toxicology; Molecular Pathways of Development; Animal Models of Cancer; and Apoptosis.